1. Field of the Invention
The invention relates to communications systems generally and, more particularly, the invention relates to an improved method for analyzing a stream of data to assure integrity of the content within the stream.
2. Description of the Background Art
In several communications systems, the data to be transmitted is compressed so that the available system bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1, refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is also incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, which too is incorporated herein by reference.
Information distribution systems utilizing information streams conforming to the above standards or subsets of the above standards are known. For example, an interactive information distribution system provided by DIVA Systems Corporation of Redwood City, Calif. is described in more detail in U.S. Pat. No. 6,253,375, issued Jun. 26, 2001 and incorporated herein by reference in its entirety. The DIVA VOD system distributes audio-visual information from a central server to individual subscribers utilizing MPEG-like information streams. The DIVA VOD system also allows subscribers to interactively control the delivery of audio-visual information streams using consumer-friendly commands, such as fast-forward (FF), rewind (REW), pause (PAUSE), play (PLAY) and the like that correspond to various tracks within the streams.
The DIVA VOD system stores content, such as movies, sporting events, television programs and the like on a server, illustratively a hard disk array, for subsequent transmission to subscribers within the system. The server is xe2x80x9cprovisionedxe2x80x9d from a remote content source. The provisioning content is typically provided as an MPEG-2 transport stream including video information and associated audio information. The content stored within the DIVA system comprises a play track, a fast forward track, a rewind track, associated audio tracks and other data related to the content stream.
It is important to ensure that the content stored on the server is error free and appropriate for subsequent transmission to subscribers. Similarly, it is important to insure that content read from the servers for transmission to subscribers request in the content is retrieved from the servers in a relatively error free manner.
Presently, most VOD systems utilize a circular redundancy check (CRC) to determine if content being stored and/or retrieved from a server is error free. If the portion of content being stored and/or retrieved from a server fails the CRC check, then an error handling routine is invoked. In the case of portions of content that are stored or retrieved out of order, such stored or retrieved portions will likely pass a CRC error check test. However, since such portions have been stored or retrieved out of order, subsequent presentation of these temporally shifted or non-contiguous portions by a subscriber will result in an unsatisfying VOD experience.
Unfortunately, CRC error checking may miss certain errors within the main or auxiliary information streams forming the content being checked.
Specifically, the CRC check will not detect an error condition where xe2x80x9ccorrectxe2x80x9d content has been stored or retrieved out of sequence (where portions of content are arranged in a sequence), thereby allowing the storage or retrieval of improper information. In either case, a user or subscriber within the VOD system may receive unrequested programming, temporally shifted programming, video information exhibiting undesirable artifacts, audio information exhibiting undesirable oral artifacts, video and audio information exhibiting poor xe2x80x9clip synchronizationxe2x80x9d and other errors.
Therefore, it is seen to be desirable to provide a method for assuring content integrity in a manner avoiding limitations of the simple circular redundancy check (CRC) typifying present VOD content server operations. More specifically, it is seen to be desirable to provide a method for performing a xe2x80x9ccontent integrity checkxe2x80x9d of content being stored or retrieved from, illustratively, a server within a video on demand system.
The disadvantages heretofore associated with the prior art are overcome by the present invention of a method providing integrity analysis of content data streams within an information distribution system.
An aspect of the present invention is a system for content-on-demand. Service provider equipment, including a session controller, an information server and a transport processor, is in communication with subscriber equipment via a distribution network. The server provider equipment is configured to provide content on-demand in response to a request from the subscriber equipment. The content is divided into a plurality of content portions severally distributed among disks of an array of disks. Each of the content portions comprises an identification field, a number field, a track-type field and a check field.